1. Field of the Invention
The present invention relates to a product structure of a display device that includes one or both of a transparent protective plate and a transparent substrate having a touch panel function which are disposed on a viewing side of a display panel.
2. Description of the Related Art
Many of display devices for home-use televisions and personal computers and information display devices installed in public facilities are liquid crystal display devices or organic electroluminescence display devices. Liquid crystal display devices are employed in a particularly wide range of products from as small ones as 2-inch monitors for cellular phones and the like to 60-inch or larger television monitors.
Most liquid crystal display devices include a thin film transistor (TFT) substrate and a color filter (CF) substrate which are 0.2 to 0.7 mm-thick, between which liquid crystal is held. Some cellular phones, digital cameras, small-sized information terminals, and other devices where a liquid crystal panel surface is frequently touched during use therefore have a transparent protective plate in front of a liquid crystal panel to prevent external mechanical forces from disturbing displayed data or breaking the liquid crystal panel.
In personal computer monitors, home-use televisions, and other similar appliances, too, where the liquid crystal panel surface is touched less frequently, the liquid crystal panel itself could be shattered if something like tableware or a toy hits the liquid crystal panel surface with a large enough force. Therefore, similarly to cellular phones, digital cameras, small-sized information terminals, and the like, some of such products as personal computer monitors and home-use televisions have a transparent protective plate 2 in front of a liquid crystal panel 1 as illustrated in FIG. 3 in order to prevent damage to the liquid crystal panel.
However, disposing the transparent protective plate 2 in front of the liquid crystal display panel 1 causes reflection of light at an interface between materials having different optical characteristics, specifically, refractive indices. In the case of a structure illustrated in FIG. 3, reflection of light is observed at an interface between the protective plate 2 and air existing in front of the protective plate 2, an interface between the protective plate 2 and an air layer 8 located behind the protective plate 2, and an interface between a first polarization plate 4 and the air layer 8. The reflection significantly impairs visibility of a displayed image especially in a bright environment.
In recent years, devices that have a touch panel functioning as an input device on the front side (viewing side) of the display panel are rapidly gaining popularity, because those devices may be operated easily and intuitively by touching a switch or other icons displayed on the display panel to be manipulated.
Touch panels are classified by operating principle into the following types.